The present invention generally relates to rotary furnaces and, more particularly, to a tilting rotary furnace system used in the reclamation of non-ferrous metals from scrap or dross and a method of operating the furnace.
There is an ever present demand for recovering usable material, such as non-ferrous metals, from scrap and waste items. During the recovery process, there are additional demands to decrease the amount of resources, especially fuel, required to convert the items into usable material and to decease the amount of waste by-product generated by the recovery process.
To date, the process of recovering non-ferrous metals, such as aluminum from batches of scrap material or dross material, is fairly inefficient. Aluminum scrap is obtained from a number of sources, such as waste aluminum from manufacturing facilities, industrial scrap, used automobile parts such as engine blocks, beverage containers and the like. Dross containing aluminum is often obtained as a byproduct from a manufacturing facility which uses molten metals. It is noted that dross typically has a lower aluminum content than scrap. Dross, as used herein, means the solid scum that forms on the surface of a metal when molten or during melting and is largely the result of oxidation, due to conversion of aluminum fines (small particles) to aluminum oxide, but also includes aluminum, dirt and impurities that rise to the surface of the mixture. Dross also includes salt and/or flux used as part of the previous melting process which can be potassium chloride (KCl), sodium chloride (NaCl) or other salt such as NaF, NaBr, KF and FBr. Dross also includes waste or foreign matter mixed with a substance or what is left as a residue after the substance has been used or processed.
Examples of non-ferrous recovery metal devices can be found in U.S. Pat. Nos. 5,527,380 and 5,540,752. However, these examples have not generated proven, repeatable results. In addition, these and other devices making up the current state of the art with regard to aluminum recovery have slow throughput (i.e., melt rate) with a low recovery rate in terms of the weight of recovered metal versus the beginning weight of the scrap. The current recovery devices and methods have relatively high conversion costs and use a considerable amount of fuel (e.g., 65 m3 of natural gas per metric ton of scrap and flux material). They also use a considerable amount of flux to retard oxidation. The current recovery devices and methods also generate a considerable amount of waste by-product in the form of slag (slat cake). The slag is generally not useful and requires disposal, which consumes valuable landfill space.
According to one aspect of the invention, a furnace system for recovering a non-ferrous metal from a charge of material containing the metal is provided. The furnace system includes a furnace chamber having walls defining a refractory chamber, the refractory chamber receiving the charge of material and the metal contained in the charge of material being heated into a flowable mode in the refractory chamber, the walls of the furnace chamber further defining an inlet passage to provide access to the refractory chamber; a rolling surface disposed on the furnace chamber adjacent the inlet passage; a door having a closed position adjacent the inlet passage and an open position to provide access to the inlet passage; a plurality of rollers disposed on the door and adapted to engage the rolling surface and allow the furnace chamber to rotate with respect to the door; and a support structure coupled to the door with a suspension; wherein the rollers and suspension are effective to maintain the door in the closed position during operation of the furnace system and during thermal expansion and contraction of the furnace chamber.
According to another aspect of the invention a furnace system for recovering a non-ferrous metal from a charge of material containing the metal is provided. The furnace system includes a furnace chamber having walls defining a refractory chamber with faceted interior surfaces, the refractory chamber receiving the charge of material, and wherein: the interior surfaces of the furnace chamber form a polygon when taken in cross-section along a longitudinal axis of the furnace chamber; the walls of the furnace chamber comprise a rear wall, a first frustum shaped end section connected to the rear wall, a second frustum shaped end section and a cylindrical mid-section disposed between and connecting the end sections, ends of the end sections proximal the mid-section having a larger radius than ends of the end sections distal the mid-section. The furnace system also includes a drive system to rotate the furnace chamber; and a burner introduced into the furnace chamber through an inlet passage of the second end section and for heating the charge of material into a flowable mode in the refractory chamber, and wherein: the burner introduces heat energy into the furnace chamber at an angle from the longitudinal axis of the furnace chamber; and the heat energy is reflected off of the interior surfaces of the furnace chamber walls during operation of the furnace system to distribute heating of the interior surfaces, thereby distributing subsequent heat transfer from the interior surfaces to the charge of material.